Package provided with a rigid lid and a valve, in particular for cooking food

ABSTRACT

The package is closed by a lid and it is fitted with a valve fixed over an opening zone of section greater than 10 mm 2 , and preferably lying in the range 30 mm 2  to 50 mm 2 , leading to the inside of the package and formed through said lid. This opening zone is either an orifice formed through a flat lid, or else a hollow chamber itself pierced by a vent orifice of small size. The valve comprises solely a flexible sheet extending over the opening zone together with a sealing compound disposed between the flexible sheet and the lid. The sealing compound is solid at ambient temperature and it passes to a non-sticky liquid state when its temperature is raised. During heat treatment, the valve opens and closes in a succession of venting sequences. The valve opens under the effect of the pressure inside the package increasing sufficiently to create an exhaust channel through the sealing compound in the liquid state spread between the lid and the flexible sheet, said channel extending between the opening zone and an edge of the flexible sheet. After partial venting through the exhaust channel, and while the pressure inside the package is still greater than the pressure outside it, the valve is caused to close by said exhaust channel closing due to the cohesion forces between the sealing compound in the liquid state and both the lid and the flexible sheet. On cooling at the end of heat treatment, the sealing compound solidifies and fixes the flexible sheet to the lid, thereby locking the valve in its closed position.

[0001] The present invention relates to a package fitted with a valve, in which package a substance is subjected to heat treatment that causes gas to be given off, said valve being in communication with at least one orifice leading into the package and co-operating with a sealing compound to enable venting to take place through said orifice during the treatment, while also preventing air from returning at the end of treatment. Such a package is usable in a very wide variety of fields such as cooking food, sterilizing equipment for single use in the medical field, and packaging pharmaceutical, medicinal, or cosmetic preparations.

BACKGROUND OF THE INVENTION

[0002] Document WO 01/09003 discloses the package of that type in which the valve is constituted by a base, a flexible sheet, and a sealing compound. The base has a hole in its center and it is totally fixed to the wall of the package so that the hole lies over the vent orifice formed through said wall. The flexible sheet is fixed in part to the base, for example along two longitudinal edges of said base. The wall of the package in which the vent orifice is formed and which thus supports the valve may be a film cover.

[0003] At ambient temperature, the sealing compound selected in that document WO 01/09003 is in the form of a solid or a paste, and during heat treatment it changes to a liquid and non-sticky state. Thus, during the heat treatment to which the package is subjected, the valve can be caused to pass repeatedly between a closed position in which the flexible sheet is pressed against the base and an open position in which the flexible sheet is spaced apart from the base. In a manner characteristic of that prior document, the closed position is obtained from a given value of pressure inside the package, which closure pressure inside the package is nevertheless higher than the pressure outside. The valve preferably opens at a relative internal pressure inside the package of the order of 10 millibars (mbar) and it closes when the pressure inside the package is about 3 mbar.

[0004] Such a package gives full satisfaction, in particular when cooking food subjected to heat treatment at a temperature greater than 60° C.

OBJECTS AND SUMMARY OF THE INVENTION

[0005] The solution proposed by the present invention gives results that are similar to those obtained by the valve of document WO 01/09003 in terms of operation and venting. However, it has the merit of being even simpler and thus less expensive, even though it is more limited in terms of application.

[0006] In conventional manner, it comprises a package which is fitted with a valve and which is closed by a lid, said valve being fitted over an orifice leading to the inside of the package and made through said lid.

[0007] In characteristic manner of the invention:

[0008] a) the lid is made of a material that is rigid or semi-rigid;

[0009] b) the valve comprises solely:

[0010] a flexible sheet extending over an opening zone formed through the lid and including the orifice; and

[0011] a sealing compound disposed between the flexible sheet and the lid; and

[0012] c) the section of the opening zone is greater than 10 square millimeters (mm²).

[0013] In addition, the sealing compound is solid at ambient temperature, when it is impermeable to gas, to liquids, and preferably also to microorganisms, and it passes to the non-sticky liquid state by a rise in temperature. Thus, during heat treatment, the valve is opened under the effect of the pressure inside the package rising sufficiently to create an exhaust channel through the sealing compound spread between the lid and the flexible sheet, said channel extending between the opening zone and the edge of the flexible sheet, and the valve is closed while the relative pressure inside the package is still positive, by said exhaust channel reclosing due to forces of cohesion between the sealing compound in the liquid state and both the lid and the flexible sheet. Solidification of the sealing compound during cooling at the end of heat treatment fixes the flexible sheet to the lid, thereby locking the valve in the closed position.

[0014] In the particular disposition of the present invention, which is indeed restricted to packages that are closed by a lid that is rigid or semi-rigid, the valve is of a structure that is particularly simple since it is made up solely of the flexible sheet and the sealing compound, with proper operation of the valve being obtainable only providing the opening zone formed through the lid is of sufficient section, not less than 10 mm².

[0015] In one variant embodiment, the opening zone is constituted by a simple vent orifice, of section greater than 10 mm², formed through a flat lid.

[0016] It should be observed that in document WO 01/09003, the vent hole has a diameter of about 1 mm, and thus a section of about 0.8 mm².

[0017] In another variant embodiment, the opening zone is constituted by a hollow chamber, e.g. formed by stamping the lid, said chamber being of section greater than 10 mm² and being pierced by a vent orifice of smaller section.

[0018] The opening zone formed in the lid preferably has a section of about 30 mm² to 50 mm².

[0019] In a particular embodiment, the lid is made of metal. In particular, it can be constituted by a lid screwed onto the top of the package.

[0020] In a particular embodiment, the flexible sheet is fixed in part, e.g. by adhesive, to the lid on either side of the opening zone while leaving at least one unfixed zone, and the exhaust channel extends between the opening zone and an edge of the flexible sheet in said unfixed zone.

[0021] In a particular embodiment, the top face of the flexible sheet is fixed, e.g. by adhesive, to a flat element of the label type, itself fixed in part to the lid on either side of the opening zone, while leaving at least one unfixed zone. Under such circumstances, the exhaust channel extends between the opening zone and the edge of the flexible sheet facing the unfixed zone of the flat element.

[0022] In a particular embodiment, where it is absolutely essential to avoid any risk of the valve being contaminated by substances contained inside the package, said package includes a porous flat element fixed over the vent hole, on the inside face of the lid.

[0023] In a particular embodiment, making it easier to open the lid, the package includes a tab fixed to or extending the flexible sheet or the label type flat element. By pulling on the tab, the user can detach the flexible sheet from the lid, thereby uncovering the opening zone in the lid, which has the effect of putting the inside of the package at atmospheric pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be better understood on reading the following description of embodiments of a package closed by a screw-on metal lid fitted with a valve constituted solely by a flexible sheet and a sealing compound, as shown in the accompanying drawings, in which:

[0025]FIG. 1 is a diagrammatic section view of a first embodiment of a package in which the portion of the lid covered by the valve is flat;

[0026]FIGS. 2 and 3 are plan views of the FIG. 1 package with its valve in the closed position (FIG. 2) and in the open position (FIG. 3) during the treatment;

[0027]FIG. 4 is a diagrammatic section view of a lid in a second embodiment of a package, in which the orifice in the lid is provided with a porous inside element;

[0028]FIG. 5 is a diagrammatic perspective view of a lid of a third embodiment of a package including an information-providing label;

[0029]FIG. 6 is a diagrammatic perspective view of the lid of a fourth embodiment of a package in which the valve is fitted with a tear tab;

[0030]FIGS. 7 and 8 are diagrammatic section views of the lid in a fifth embodiment of the package in which the portion of the lid covered by the valve includes a hollow chamber constituting the opening zone, the valve being shown in its initial position in FIG. 7, and being shown in its closed position after heat treatment and sealing in FIG. 8; and

[0031]FIG. 9 is a diagrammatic section view of the lid of a sixth embodiment of the package in which the opening zone of the lid is a hollow chamber in the form of an annular bulge.

MORE DETAILED DESCRIPTION

[0032] The package 1 in the first embodiment shown in FIG. 1 is constituted by a jar 2 and by its rigid or semi-rigid closure lid 3, suitable for screwing in leaktight manner onto the top portion 2 a of the jar 2. The lid 3 is pierced by an orifice 4 which is designed to allow the gas which is produced in the inside portion 5 of the package 1 to escape while the substances 6 contained inside the jar 2 are being subjected to heat treatment.

[0033] The orifice 4 made in a flat portion of the lid 3 is a circular hole having a diameter of several millimeters, preferably being about 7 mm, which corresponds to a section of about 38.5 mm².

[0034] A flexible sheet 7 is placed over the orifice 4, and in the example shown the sheet is of rectangular or square configuration. The flexible sheet 7 is preferably fixed solely along two side zones 7 a, 7 b adjacent to two opposite sides 8 a and 8 b of the sheet 7 on either side of the orifice 4. The sheet 7 is fixed by an adhesive coating 9 interposed between said two side zones 7 a and 7 b and the lid 3. Between the two fixing zones 7 a and 7 b there are two unfixed zones 10.

[0035] A sealing compound 11 is placed between the flexible sheet 7 and the lid 3. This sealing compound must present the feature disclosed in document WO 01/09003 of being solid (or possibly a paste) at ambient temperature, in which case it should be impermeable to gas, to liquid, and preferably also to microorganisms, and it must be capable of passing to a non-sticky liquid state when its temperature is raised.

[0036] The sealing compound 11 is preferably selected from a group comprising the following in pure or mixed form: paraffins; compounds presenting paraffin-like behavior with setting temperatures at which macro-crystals are formed; micro-crystalline waxes; and paraffins containing additives. The compound may comprise a paraffin or a compound presenting paraffin-like behavior with a setting temperature lying in the range 48° C. to 53° C., and in particular lying at 51° C. It may be a micro-crystalline wax whose melting point lies in the range 64° C. to 72° C. It may be a paraffin containing additives with a melting point lying in the range 65° C. to 70° C.

[0037] The sealing compound 11 is preferably placed on the inside face of the flexible sheet 7. This may be done by continuous coating while omitting the fixing zones 7 a and 7 b, or possibly by non-continuous coating, as represented by shading in FIG. 2, with the zone overlying the orifice 4 not being coated. Nevertheless, this is not an exclusive feature of the invention, and the sealing compound 11 can be placed between the flexible sheet 7 and the lid 3 in the form of a drop.

[0038] The operation of the valve 12 is based on the behavior of the sealing compound 11 and on capillary forces between said sealing compound 11 when in the liquid state and both the lid 3 and the flexible sheet 7.

[0039] During heat treatment, the sealing compound 11 which is in the solid (or possibly paste) state passes to the liquid state when the temperature goes through the setting temperature or reaches the melting point of the sealing compound 11. In the liquid state, said compound spreads by capillarity over the entire available area of the valve 12 between the flexible sheet 7 and the lid 3. Given that this rise in temperature takes place together with a rise in the pressure in the inside portion 5 of the package 1, the sealing compound 11 in the liquid state cannot penetrate through the orifice 4 since it is pushed away therefrom by said pressure.

[0040] So long as the forces due to internal pressure are smaller than the cohesion forces due to the capillarity which spreads the sealing compound 11 in the liquid state over the entire unfixed zone 10, the valve 12 remains closed. Nevertheless, the inside portion 5 of the package 1 is at a pressure which is higher than the pressure outside the package, thus eliminating any risk of the substance 6 contained inside the package 1 being contaminated since there is no possibility of air being sucked into the package.

[0041] When the pressure in the inside portion 5 of the package 1 increases, and more particularly when the forces exerted by said inside pressure exceed the capillary cohesion forces between the layer of sealing compound 11 in the liquid state and the two walls formed by the flexible sheet 7 and the lid 3, said two walls become separated because the sealing compound in the liquid state is pushed out of the way, thereby creating an exhaust channel 13. The channel extends between the orifice 4 and the edge 18 of the sheet 7 corresponding to the unfixed zone 10, as can be seen in FIG. 3. Gas is vented to outside the package 1 via the exhaust channel 13. When the inside pressure decreases because of the venting, and reaches a given value, which value nevertheless still corresponds to the inside pressure being higher than the outside pressure, then the action of the capillary cohesion forces becomes greater again than the action of the forces exerted by said pressure, thereby causing the sealing compound 11 in the liquid state to move in the opposite direction, which tends to close said exhaust channel 13.

[0042] The exhaust channel 13 closes progressively, as a function of the decrease in inside pressure, thereby providing a degree of regulation to the rate at which gas is vented.

[0043] Once the exhaust channel 13 has reclosed, the valve 12 is in its closed position even though the sealing compound 11 is still in the liquid state. Throughout the heat treatment, the valve 12 opens and closes on successive occasions in the manner descried above, corresponding to a succession of venting sequences.

[0044] At the end of the heat treatment, the package is cooled down, thereby reducing the pressure inside the package 1 and confirming closure of the valve 12, with the sealing compound 11 passing from the liquid state to the solid or paste state, thus locking the valve 12, and finally a partial vacuum is established in the inside portion 5 of the package 1.

[0045] In order to guarantee the operation as described above, and given that the flexible sheet 7 is held on the lid 3 by the capillary forces of the sealing compound in the liquid state, it is important to ensure that the forces exerted by the inside pressure act over a large area of the flexible sheet 7. That is why it is necessary to ensure that the orifice 4 formed through the flat portion of the lid 3 and which serves as an opening zone thereto is of large section, of the order of or greater than 10 mm².

[0046] In a particular embodiment where the lid 3 is a totally rigid metal lid, the orifice 4 is a circular hole having a diameter of 7 mm, giving a section of about 38.5 mm². A hole having a diameter of 1 mm would not enable the valve to operate in the manner described above.

[0047] In a second embodiment as shown in FIG. 4, the lid 3 is provided on its inside face 14 with a porous element 15 which is fixed over the orifice 4. The porous element 15 is designed to allow gas to vent from the inside portion of the package while preventing any possibility of contamination between the valve 12 and the substances contained in the package. This porous element 15 must therefore be impermeable to liquids.

[0048] In the third embodiment shown in FIG. 5, the flexible sheet 7 is not fixed to the lid 3, but to a label 16 which is used for informing the consumer about the substance contained in the package. The flexible sheet 7 is fixed to the label 16, for example, by sticking the top face 7 c of the flexible sheet 7 to the bottom face of the label 16. The label 16 is in turn fixed in part to the lid 3 so as to leave at least one unfixed zone. While the valve 12 is in operation, the exhaust channel formed through the sealing treatment in the liquid state extends between the orifice 4 and the edge of the sheet 7 a which faces the unfixed zone of the label 16.

[0049] In the fourth embodiment shown in FIG. 6, the package has a tear tab 17 which extends or is fixed to the flexible sheet 7 of the valve 12. Given that at the end of cooling a vacuum is established inside the package, opening the lid 3 requires additional force to be exerted to overcome this vacuum. By using the tear tab 17, the user can easily remove the flexible sheet 7 from the orifice 4, thereby reestablishing pressure equilibrium between the inside portion of the package and ambient air. This makes it easier to open the package.

[0050] In the fifth embodiment shown in FIGS. 7 and 8, the portion of the lid 3 to which the valve 12 is fitted is not totally flat, but presents an indentation or hollow chamber 18 which constitutes the opening zone of section greater than 10 mm², over which the flexible sheet 7 extends together with the sealing compound 11 constituting the valve 12. In the example shown, this hollow chamber is formed by stamping the material constituting the lid 3. It is slightly conical in shape. In addition it is an open chamber, leading to the inside of the package via a vent orifice 19 which is formed in the lid 3 through the bottom wall 20 of the hollow chamber 19. This orifice 19 is a circular hole of section that is much smaller than the section of the hollow chamber 18. For example, it is a hole having a diameter of 2 mm, which corresponds to a section of about 3.15 mm².

[0051] As in the first example, the flexible sheet 7 is held in place by adhesive coating 9 in two side zones 7 a and 7 b.

[0052] The valve 12 in this fifth embodiment operates identically to that described above for the first embodiment. The internal chamber 18 is in communication with the inside of the package through the orifice 19 and the action of the forces exerted by the internal pressure bears against the surface of the flexible sheet 7 facing the internal chamber 18, which acts as the opening zone of section of about 10 mm² or greater.

[0053] The essential difference between the first and fifth embodiments lies in the last step of locking the valve during cooling after heat treatment. This step is illustrated in FIG. 8. At the end of heat treatment, during cooling of the package, there is both a reduction in temperature which causes the sealing compound 11 to pass from the liquid state to a solid or paste state, and also a reduction in the internal pressure inside the package which creates a certain amount of vacuum, and thus a level of suction in the hollow chamber 18, which suction causes the flexible sheet 11 to become deformed and press against the bottom wall 20 of said hollow chamber 18 over the vent orifice 19. This improves the locking of the valve 12 because of the larger contact area between the flexible sheet 7 and the lid 3 due to said sheet being pressed against the bottom wall 20 of the hollow chamber 18. In the first embodiment, this contact area is restricted to the portion of the flexible sheet surrounding the orifice 4.

[0054] This variant embodiment is advantageous because in the event of pressure rising again inside the container, e.g. because it is squeezed or because it becomes deformed on being dropped, there is much less risk of the valve opening in untimely manner. This does not prevent the valve opening again subsequently when temperature is raised. Under such circumstances, the sealing compound returns to the liquid state thus allowing the flexible sheet to return to its initial shape and allowing the valve to open as soon as the pressure inside the container has increased sufficiently.

[0055] The configuration of the hollow chamber 18 and also the number of orifices 19 and the sizes thereof may vary as a function of requirements.

[0056]FIG. 9 shows another embodiment in which the hollow chamber 18 is formed by an annular bulge 21 surrounding a projecting portion 22 in which the small-dimension vent orifice 23 is formed. In this variant, the vent orifice 23 is even better protected against contamination.

[0057] It should be observed that it is not absolutely essential for the flexible sheet 7 to be fixed to the lid 3 by external fixing means such as a coating of adhesive. The flexible sheet 7 can be secured to the lid merely by the sealing compound, because of the action of capillary force when the compound is in the liquid state, and providing said compound adheres to the flexible sheet and to the lid when it is in the solid state, thereby acting as an adhesive coating.

[0058] It should also be observed that the sealing compound implemented in the present invention presents a phase change that is reversible between its solid phase and its liquid phase. This disposition enables the valve to operate if the package is heated again subsequently, for example immediately before consuming the substance it contains, without that leading to any risk of excessive pressure rise. The package of the present invention makes it possible to limit the risk of being burnt that can occur when a consumer heats a closed package containing a precooked meal, for example, where burning is due to hot food being squirted out during opening, or even to the container exploding. As mentioned above, when a package of the invention has been subjected to heat treatment followed by cooling, it presents a partial vacuum in its head space, i.e. the space lying between the substance and the lid. When the consumer reheats the package in order to eliminate the partial vacuum and reestablish positive pressure inside the package, it is necessary for the temperature to be raised to a level higher than that of the first heat treatment, with the sealing compound then again being in the liquid phase, and the valve can be opened as soon as the inside pressure is sufficient, with gas venting.

[0059] Nevertheless, it is not possible to avoid all risks, particularly when a consumer performs reheating under conditions that are too sudden, for example using boiling water or in a household microwave oven operating at a power of 800 watts.

[0060] To avoid such risks altogether, it is preferable for the flexible sheet to be made of a material that is suitable for deforming permanently when subjected suddenly to excessive temperature and/or pressure conditions. Thus, the valve operates properly as described above during first heat treatment under conditions that are relatively gentle. If the package is subsequently reheated under conditions that are too sudden, for example by being plunged into boiling water or placed in a microwave oven operating at about 800 watts, then the flexible sheet deforms under the effect of the temperature and/or the pressure, thereby creating an exhaust channel that is permanent. This thus provides the option of venting a very large amount of gas instantaneously, and consequently even if an unopened package is subsequently cooled, no partial vacuum is established with the accompanying possible deformation of the package. For example, a flexible sheet made of polyester having thickness of less than 25 micrometers (μm) presents permanent deformation under temperature and pressure conditions that are too sudden. 

What is claimed is: 1/ A package fitted with a valve and closed by a lid, said valve being fitted over an orifice leading to the inside of the package and formed through said lid, wherein: a) the lid is made of a material that is rigid or semi-rigid; b) the valve comprises solely: a flexible sheet extending over an opening zone formed through the lid and including the orifice; and a sealing compound disposed between the flexible sheet and the lid; c) the section of the opening zone is greater than 10 square millimeters (mm²); and d) wherein the sealing compound is solid at ambient temperature, when it is impermeable to gas, to liquids, and preferably also to microorganisms, and passes to a non-sticky liquid state when its temperature is raised so that during heat treatment the valve opens and closes in a succession of venting sequences, with opening of the valve being obtained under the effect of the pressure inside the package rising sufficiently to create an exhaust channel through the sealing compound then in the liquid state and spread between the lid and the flexible sheet, said channel extending between the orifice and an edge of the flexible sheet, and closure of the valve being obtained, after partial venting via the exhaust channel and while the pressure inside the package is still greater than the pressure outside, by said exhaust channel reclosing due to the cohesion forces between the sealing compound in the liquid state and both the lid and the flexible sheet, so that during cooling after the heat treatment, solidification of the sealing compound fixes the flexible sheet to the lid, thereby locking the valve in the closed position. 2/ A package according to claim 1, wherein the opening zone is constituted merely by a vent orifice of section greater than 10 mm² formed through a flat lid. 3/ A package according to claim 1, wherein the opening zone is constituted by a hollow chamber, e.g. formed by stamping the lid, said chamber being of section greater than 10 mm² and being pierced by a vent orifice of smaller section. 4/ A package according to claim 1, wherein the opening zone made through the lid has a section of about 30 mm² to 50 mm². 5/ A package according to claim 1, wherein the flexible sheet is fixed in part to the lid on either side of the opening while leaving at least one unfixed zone. 6/ A package according to claim 5, wherein the valve has two unfixed zones opposite each other between the flexible sheet and the lid. 7/ A package according to claim 1, wherein the lid is made of metal. 8/ A package according to claim 7, comprising a jar and a lid fixed in leaktight manner by being screwed onto the top portion of the jar. 9/ A package according to claim 1, wherein the top face of the flexible sheet is fixed, e.g. by adhesive, to a flat element of the label type, itself being fixed in part to the lid on either side of the opening zone, while leaving at least one unfixed zone. 10/ A package according to claim 1, including a flat porous element fixed over the orifice on the inside face of the lid. 11/ A package according to claim 1, including a tab fixed to or extending the flexible sheet or the flat label-type element. 12/ A package according to claim 1, wherein the flexible sheet is made of a material that deforms permanently under conditions of temperature and pressure that are too sudden. 13/ A package according to claim 12, wherein the flexible sheet is a sheet of polyester that is less than 25 μm thick. 